I used to develop in C and C++, back then the software ran on a single machine, and the most common performance issues we faced were unintentionally introducing

I used to develop in C and C++, back then the software ran on a single machine, and the most common performance issues we faced were unintentionally introducing some O(N^2) complexity, usually within a deep call stack. Today I develop mostly in Python on a web backend system. Now, the most common performance issues I see are making multiple network calls when one would suffice (e.g., not caching repeated database queries). I have no doubt that there are many hidden O(N^2) issues lurking in the python code, but because network calls are so expensive, they seem to dominate optimization efforts. I suspect that I'm not alone here, as today, there are many I/O performance tools than there were in the past.